In days of old... during world war II and the korean war, there was a shortage of men to do labor. The guest workers were used to fill in for the men at war.
That worked fine. For many years however, growers tried hard to use illegal aliens to do labor on their farms. They loved it because they could put them up in shanty's, ignore work place rules, use pesticides in manners that were not safe, and generally abuse illegal aliens who could not read the warnings on the barrels of poison. To a limited point, those days are gone. We still have very crooked rats who use illegal aliens when American Workers would call the law in a second. So now we turn to ... guest workers... as a means to get seasonal temporary workers in a way other than, for example, the human resources department.
They put American Workers out of a job, and they work for less while living, seasonally, in very shabby barracks. Some, and it has always only been some, of the ratso employers will abuse those laborers because theycannot speak English. Almost always, in addition, Mexican Nationals cannot read English even while they speak it rather well. And certainly cannot write English.
So guest workers put more money into the growers pockets while it moves American Workers into Welfare. BUT.. to the second part of your question, if guest workers are used, the taxes are collected on the wages, and taxes collected from the employers.
Illegal aliens will work under the table in a heartbeat. That means fewer taxes and the potential to abuse the Mexican/Guatemalan illegal aliens.
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Overall, these guys are playing with billions of dollars throughout the United States. And the taxes at the local level, are most certainly serious. Further, the illegal aliens with their Mafia I.D.'s, can take advantage of welfare as well as all the infrastructure that exists in this country. (Hospitals, schools, emergency services, etc.)
References...
http://www.fairus.org
http://www.cis.org
http://www.illegalaliens.us
Do a search for the Heritage Foundation and select immigration.

Have you even started thinking about any of these?
One effect of the industrial revolution was that it greatly increased material wealth and hence made it economically feasible for more kids to go to school instead of work, whether on the farms or as apprentices. Why we even have child labor laws forcing kids to go to school rather than work.
Unfortunately, ....

Plutocracy (rule by the wealthy, or power provided by wealth) does not affect a truly free market economy. It can and does affect an economy when government has power to overrule the market in some way. Businesses become rent-seekers who obtain government favors and protection in return for political contributions and support. Rent-seeking transfers resources from the public at large to those who obtain the protection form government.
Examples of key figures?
Plutocracy was a term used by European fascists to describe how Jews supposedly controlled the economy.
Warren Buffet used his monetary and political power (kissing up the President) to obtain an incredibly favorable deal with B of A (whose viability is now essentially government-guaranteed).
Power and wealthy farming interests obtain subsidies and tariffs which direct money to them form consumers.
Large banking interests get the government to call them "too big to fail", which means that their cost of funds will be lower than their competitors.
Teachers unions use their power and wealth to obtain protection for their cash flow.
Trial lawyers use their wealth to obtain legislation that ensures ever increasing amounts of litigation.